Decomposition of sodium aluminate liquor



H. TIEDEMANN DECOMPOSITION OF SODIUM ALUMINATE LIQUOR Filed Oct. 2, 1940 INVENTOR; Hans fieaemalm Patented July 31; 1945 A DECOMPOSITION F mo InG ODIUM 'ALUMINATE UOR ' Hans Tiedemann, Tokyo, Japan; vested in the Alien Property Custodian Application October 2, 1940. sei-iei No. 359,350

ermany December 21, 1937 2 Claims. (01; 23-143) The present invention refers to'a process and apparatus for the production of aluminum hydroxide.

By the well known Bayer method sodium aluminate solutions are prepared from bauxite and caustic soda; after hydrate of alumina has been added as inoculator these solutions are stirred for three to six days whereby 50 to 60% of the a1uv mina is precipitated as hydrate due to hydrolytic action. I

This decompo'sitionof sodium aluminate solutions is usually carried-out in high steel tanks of tinuously carriedback towards the feed whereby the precipitation is accelerated.

A further advantage of the present invention consists therein that the precipitated particles of ln'drate of alumina'can-be' settled in a quiet zone subsequent to the reaction zone from which they,

. can be easily removed.

5 to 8 meter diameter and 8 to 12 meter height which are provided with agitator mechanisms supported on vertical shafts.

These unusually large agitator tanks require huge investment and foundation costs and require a considerable power for their operation. Usually they have to be operated discontinuously which represents a further disadvantage as the subsequent steps of the process can be done con- 5 tinuously.

It is an object of this invention to avoid the aforesaid disadvantages and to obtain a continuous andspeedy precipitation and production of aluminum hydroxide from aluminate liquors.

It is a further object of the invention to greatly simplify the equipment for stirring-out the aluminate liquor-and to reduce at the same time the costs of installation and of operation.

It is a further-object of the invention to feed a and to transport the aluminate liquor through a combined reaction or precipitation and a subsequent settling zone and to prevent the settling of the precipitated aluminum hydroxide particles in the reaction zone.

It is 'a further object of the invention to effect the precipitation or the aluminum-hydroxide par- 1 ticles from the aluminate liquor within the reacting zone by revolving agitation and to recirculate a bottom portion of the aluminum hydroxide particles loaded liquor to the teed inlet.

The invention may be advantageously carried out in a flat tank wherein-by means of suitable agitating devices a horizontal main stream and near the bottom of the tank a secondary stream in opposite direction to the main stream is created which prevents the settling of theprecipitatedhydrate particles on the bottom of the tank below the agitating mechanisms and which again combines with the main stream on the feed side of the tank at the upper level of the liquid body.

In this way a partial circulation of the liquor is created in the tank by which apart or the formed particles of hydrate of alumina is con- In large installations several of these longitu dinal basins can be combined to one basin with proper partitions in-between. The retention time of the solution can be varied by suitable'closing mechanisms by which difl'erent parts of the basin can be eliminated from operation. The addition of the inoculator can also be accomplished by recirculation of a part of the decomposed solution or by subsequent classification and recirculation of the fine hydrate portion.

Thebasins for example can be made of concrete which could be covered by thin steel plate or by other suitable alkali-proof materials.

High costs for foundation of the heretofore lmown agitator tanks are not required. The agitating mechanism according to the present invention requires low investment costs 'and has a low power'demand. Repairs can be done easily. The

continuous operation can easily be supervised and gives uniform results.'-

The manner of operating the present method Q is illustrated by way of example in the attached. drawing of which Fig. 1 shows a vertical section through the basin with agitating mechanism, 1

Fig. 2 represents a top view.

The aluminate liquor is fed as top la'yerirom the launder H into a flat basin i2 which forms the stirring-out or reaction zone. By the application or this zone of revolving agitation mechanisms two streams l5, it are created which now in difierent and oppositedirections. The stream is the main stream of the liquid. The recirculated bottom stream' l5 flowing in a direction opposite to the main stream is'sumciently strong to prevent the settling of hydrate of alumina on the bottom of the basin. 7 The stream is c reated by therotation of the paddle-wheels l8, ll, l8,

l9 whicl -otate in the same direction.

The fresh liquor emerging from the launder ll hits the stream it when entering the basin I2 and hereby reaches a zone of high particle concentration. A major section 01' the solution continues to now through the-basin and the am minu-m hydroxide particles are transported into the settling zone at the end 'of the tank where there are no asitator mechanisms.

Another portion of the stream it o deflectedtowards thebottomoithetsnkbymeans-oithe paddle-wheels and is recirculated as stream ii. This current ll carries particles of hydrate of alumina which are thus transported towardsthe irontendoithebasinortank i2. 'I'herethe streamisdeflectedagainvmtowardsthemain stream it. By this alteration of direction or the current continuously crystallization centers or nuclei are added to the fresh stream 01' solution wheelby the precipitation 01' the hydrate is accelera The tank-l2 has a bottom 24, side walls 28, 20 and a front wall 21. The discharge end 0! the basin is not shown in the drawing. Inside the basin the paddle-wheels it to I! are arranged. The number and arrangement of these paddle wheelsinsidethetankeanoicoursebevuied in wide limits. Across the basin I! are shaft: 28

which may be supported on columns a. In the shaft 20 is a sprocket 3| which is driven.by a chain-l2 and a sprocket II from the geared motor 34. The shaft 28 of the paddle-wheel it is provided with another sprocket 81. From this sprocket the sprocket 3! and the shaft 2! of the next paddle-wheel i1 is driven by a chain 38. In this way a single motor can be used for, driving all paddlerwheels."

The shaft a of the with several arms 4|, II which carry the opp paddles 42, 43. Die paddle wheel it consists of several such units which are designated with A.

B, C, D,- E. Each paddle has diagonal reinforcing, elements M which assist in themixinsn The agitator mechanisms II, n, is, II are of the same design with the only diflerence that the paddlesoi the subsequent are staggered by 90. The paddles o! the mechanism il may be somewhat narrower than those of mechanism II. In the same way also paddles o't mechanlsmil may he narrower than those of the mechanism il andthose oi the mechanism ll narrowerthanthoseotthemechanismll.

- .Preierably the feed openings 28 shouldnot be located lower thanthe horizontal plane in which paddle-wheel It is provided' assasos .scne.

the shafts II are situated. If these openings were located at a low lcvelthe incoming stream 0! solution would collide with the returning circular The agitating machanisms have to be arranged suiiicientlyelosetothebottomllsothatno settling 01' particles on said bottom may occur which may counteract the circular illowv oi the liquid. Y

I claim:

1. A method for producingaluminumhydroxide from aluminate liquor comprising flowing the liquor into a list decomposition and settling tank having separate contiguous decomposition and settling zones, agitating the liquor in the decomposition zone by a series of substantially submer ed membersrevolving about a horizontal axis in such manner that localized zones of agitation are established and that a flow of liquor and sus- 'pended aluminlimhydroxide particles substantially in the directions! the feed into the settling zone and a return flow of the liquor and suspended alumlnumhydroxide particles in layers above the bottom towards the feed and a mixing of the return liquor with the feed are eilected.

2. A method for producing aluminumhydroxide from aluminate liquor comprising flowing the liquor into a hat decomposition and settling tank having separate contiguous decomposition and settling sones, agitating the liquor in the decomposition zone by a series 01 substantially submerged members. revolving about a horizontal,

axis in such-manner that localized zones oi. agitation are established and that .a now of liquor and suspended aiuminumhydroxide particles substantially in the direction of the feed into the settling sons, a return now of the liquor and sllsa pended v aluminumhydroxide particles substantiallyinthedirsctionortheieedintothesettling oi the return liquor with the teed are effected and settling the aluminumhydroxide in the settlins 

